1. Field of the Invention
The present invention relates to delay lines used for delaying signal transmission in computers, measurement apparatuses, and the like. More specifically, the invention relates to delay lines in which delay time can be adjusted.
2. Description of the Related Art
FIG. 9 is a top view of a prior art example of a delay line. A delay line 80 has a structure in which a transmission line 82 used for a signal line is folded in a meandering manner and disposed on one of the main surfaces of a dielectric substrate 81, and a ground conductor (not shown) is disposed on substantially all of the other main surface of the dielectric substrate 81. The ends of the transmission line 82 are connected to an input terminal 83, and an output terminal 84, respectively. The entire length of the transmission line 82 determines the delay time between the input terminal 83 and the output terminal 84. In order to change the delay time, as shown in FIG. 9, an intermediate tap terminal 85 is disposed at a certain point on the meandering transmission line 82 and used, for example, as an output terminal, thereby providing a different delay time. The intermediate tap terminal 85 is adapted to be connected to the transmission line 82 at different positions, whereby the delay time can be changed by changing the position.
However, in the case of the above delay line, when the position of an output terminal has been set according to a desired delay time, it is impossible to adjust the delay time again, after the delay line has been mounted in a printed circuit board or the like.
In addition, since one of the three terminals is not used, the unused terminal generates a capacitance or works as a stub, which leads to a problem of causing the reflection of a signal.
In addition, as shown in FIG. 9, when a transmission line to be used has a meandering configuration, an intermediate tap terminal can be connected only to the lower-side curved part of the meandering transmission line. As a result, it is impossible to adjust delay time continuously.